.alpha.-1,6-Glucosidases are enzymes which cleave the .alpha.-1,6-glucoside bond in starch etc. to produce straight chain amyloses. They are classified by substrate specificity primarily into isoamylase (EC 3.2.1.68) and pullulanase (EC 3.2.1.41), etc. Pullulanase is widely employed in combination with endo-type amylases and exo-type amylases in the production of malto-oligosaccharides, such as glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, etc.
While .alpha.-1,6-glucosidase-producing microorganisms have been previously found amongst yeast, various bacteria have recently been reported to be capable of producing an .alpha.-1,6-glucosidase. Bacteria capable of producing an .alpha.-1,6-glucosidase which have been reported thus far include, for example, Aerobacter aerogenes, Escherichia intermedia, Pseudomonas amyloderamosa, Streptococcus mitis, and genera Cytophaga, Streptomyces and Flavochromogenes.
Microorganisms belonging to the genus Bacillus and capable of producing an .alpha.-1,6-glucosidase include Bacillus cereus IFO 3001, Bacillus fermus IFO 3330, Bacillus acidopullulyticus, and Bacillus sectorramus.
The optimum pH of most of the known .alpha.-1,6-glucosidases is in a neutral to weakly alkaline region. Therefore, disadvantages arise in the field of saccharification where reactions are conducted in an acidic region.
On the other hand, .alpha.-1,6-glucosidases having their optimum pH in an acidic region thus far reported include those produced by Pseudomonas amyloderamosa, Bacillus acidopullulyticus, and Bacillus sectorramus. However, the enzymes produced from the first two of these microorganisms are not heat resistant, which is industrially disadvantageous, or a long cultivation time is required for these bacteria to obtain a substantial amount of the desired enzyme, which is economically disadvantageous. Bacillus sectorramus and the .alpha.-1,6-glucosidase produced therefrom were reported as being free from these disadvantages. However, development of an .alpha.-1,6-glucosidase with industrially advantageous properties is still required.